1. Field of the Invention
The present invention relates to a power supply device that includes a plurality of battery cells arranged side by side with separators being interposed between the battery cells, and a vehicle using the power supply device.
2. Description of the Related Art
A power supply device or a battery system has been developed that includes a number of battery cells arranged side by side, and forcedly blows air to cooling gaps between the battery cells. This type of power supply device or battery system is used for vehicles such as hybrid car and electric vehicle. Since this type of power supply device employs a number of battery cells, the battery cells will have a temperature difference among them. In particular, in the case where the number of the battery cells arranged side by side is large, it is difficult to cool all the battery cells to even temperatures, in other words, to temperatures that fall within a small range. It is very important for a vehicle battery system including a number of battery cells arranged side by side to reduce the temperature difference among battery cells to be as small as possible. The reason is that temperature difference may cause uneven remaining capacities of the battery cells, and as a result may deteriorate the life of some of the battery cells. The efficiency of batteries in charging/discharging operation varies in accordance with their temperatures. For this reason, in the case where batteries have temperature difference, even if the batteries are charged/discharged at the same current, the batteries will have different remaining capacities. If the batteries have different remaining capacities, when a battery is likely to have a larger remaining capacity, the battery is likely to be overcharged. On the other hand, when another battery is likely to have a smaller remaining capacity, the battery is likely to be over-discharged. If a battery is overcharged or over-discharged, the battery will deteriorate faster. As a result, the life of the vehicle battery system will be reduced. In particular, in the case of the vehicle battery system for hybrid car, plug-in hybrid car, electric vehicle and the like, since a number of side-by-side arranged batteries are provided to be charged/discharged at a large amount of current, its manufacturing cost will be very expensive. For this reason, it is important for the vehicle battery system to increase its life. In particular, as the number of batteries used in the vehicle battery system increases, its manufacturing cost increases. Also, from this viewpoint, it is required to increase the life of the vehicle battery system. Contrary to this, as the number of side-by-side arranged batteries increases, temperature difference in the vehicle battery system will increase, which in turn may reduce the life of vehicle battery system.
A vehicle battery system has been developed that includes a plurality of battery cells arranged side by side, and forcedly blows cooling gas to cooling space between the battery cells (Japanese Patent Laid-Open Publication 2007-250515).
In the vehicle battery system disclosed in JP 2007-250515 A, as shown in a cross-sectional view of FIG. 25, cooling gaps 103 are formed between battery cells 101 of a battery block 110, and inlet and outlet ducts 106 and 107 are provided on the both sides of the battery block 110. The vehicle battery system forcedly blows cooling air through the inlet duct 106 to the cooling gap 103 so that the cooling gas is discharged through the outlet duct 107. Thus, the battery cell 101 is cooled.
However, in the system in which the battery cells are cooled one after another by the cooling air, although a battery cell located closer to the inlet duct is cooled well by cold cooling air that just arrives at this battery cell, the cooling air is forcedly moved and is gradually heated by repeated heat exchange between the cooling air and battery cells. For this reason, there is a problem in that, when battery cells are arranged side by side in the longitudinal direction of a cooling duct, temperature difference will arise due to the positional difference among the battery cells. Such temperature difference among the battery cells may cause property deterioration difference of life difference among the battery cells. In particular, the output of the battery system is restricted in accordance with a battery cell having the lowest temperature. For this reason, in order to maximize the performance of the battery system, ideally, it is desired to bring ΔT (the difference between the highest and lowest battery temperatures) to zero.
The present invention is devised to solve the above problem. It is a main object of the present invention to provide a power supply device that can reduce temperature difference among battery cells and maximize the performance of the battery cells.